[SI-LIST] Re: Probe impedance effect at high frequency
- From: David Instone <dave.instone@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Fri, 17 Mar 2006 10:21:02 +0000
Hal, I totally agree with you that a high impedance probe is not
required. However, you will see what is happenning on your power rails
a lot better with a good diff probe than with just coax, and it will be
quicker 'cos you won't need the soldering iron :-) . While probably
not being a completely technical explanation think of it as being akin
to a 4 wire ohms measurement, in particular it eliminates the effect of
any connection the to the scopes ground to UUT ground via their
respective PSU's and safety grounds etc.
But don't take my word for it, try it.
Dave
Hal Murray wrote:
>>But if you want to probe the power rails to look at the noise
>>characteristic better to use a high impedance probe.
>>
>>
>
>Why?
>
>Why not go direct with 50 ohm coax and maybe a DC blocking cap? There isn't
>going to be any problem with the scope loading down the signal.
>
>
>
>
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